Screen goes black and channel unavailable, can’t rewind spontaneously

I’ll be watching a show and all of a sudden the screen goes black then a couple seconds later a message pops up saying “channel is unavailable try again “ . Sometimes it reloads within a couple seconds but most of the time I try to change channel after waiting a little bit and sometimes it will let me change and sometimes it won’t.  Sometimes the channel I change to is working and sometimes it says same message. Usually I have to unplug box to reset it . 
Another issue is sometimes when I go to rewind it shows on the bar at the bottom there is no data like I just started watching show. Other times it will say “action is not supported “ any ideas to help with this problem would be appreciated!